Electrodeposition of silver antimony alloys



United States Patent Ofiice 3 ,425,9 1 7 Patented Feb. 4, l 969 3,425,917 ELECTRODEPOSITION F SILVER ANTIMONY ALLUYS Hubert Olfermanns, Solingen-Merscheid, and Willi Skaliks, Berlin, Germany, assignors to Schering A.G., Berlin Germany No Drawing. Filed Apr. 5, 1965, Ser. No. 445,701 Claims priority, application Germany, Apr. 10, 1964,

Sch 34,943 US. Cl. 204-43 Int. Cl. C23b /24 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the electrodeposition of alloys of silver and antimony, to electrolytes for use in such electrodeposition, to antimony compounds suitable for preparing the electrolytes, and to a method of making the antimony compounds.

Silver deposits obtained by electrolysis of the commonly known complex cyanide solutions are relatively soft. Silver alloys containing minor amounts of antimony can be electrodeposited by known processes and may have hardnesses as high as 200 kp./mm. and higher. Such alloy electrodeposits retain their hardness even when heated to 200 C.

Heretofore, alkali metal antimonates were added first to conventional cyanide type silver plating solutions for producing silver-antimony alloys by electrodeposition, but such electrolytes have a limited useful life increasing pH. Attempts havetherefore been made to find organic complex forming agents for making antimony stock solutions which do not unduly shorten the life of a silver plating bath. Hydi'oxy acids such as tartaric acid, aliphatic polyhydroxy compounds such as ethylene glycol, glycerol, and sorbitol, and aromatic polyhydroxy compounds such a pyrocatechol-3, S-disulfonic acid were heretofore suggested as antimony complexing agents.

It has now been found that antimony compounds, and particularly antimony trichloride, readily form complex compounds with certain alkanolamines. The complex compounds are stable, readily soluble in water and in the usual cyanide silver plating solutions, and are excellent hardening and brightening agents for silver deposited from such electrolytes.

The alkanolamines of the invention do not unfavorably affect the properties of the electroplating solutions even when present in relatively large amounts, and they do not form harmful decomposition or reaction products during operation of the plating solutions.

The compounds which form antimony complexes suitable for the purposes of this invention generally are tertiary amines of the formula R2 RiN\ Rs (K wherein R is either lower alkyl or a radical of the formula n zn) and R and R are radicals of Formula II, n in that formula being an integer between two and six.

The following alkanolamines have been found readily to form antimony complexes which are useful addition agents for deposition of bright, hard silver-antimony alloys from otherwise conventional silver plating solutions:

Triethanolamine, tripropanolamine, tri-isopropanolamine, tributanolamine, tri-isobutanolamine, tripentanolamine, tri-a-ethylpropanolamine, trihexanolamine, methyldiethanolamine, diethanolpropanolamine, ethyldiethanolamine, methyldipropanolamine, ethyl dipropanolamine, propyldiethanolamine, and n-butyldiethanolamine.

Triethanolamine is most readily available among the tertiary amines listed and silverplating solutions containing antimony as the triethanolamine complex have been found to yield brighter alloy deposits than can be produced with the other amines listed. Triethanolamine therefore is preferred. It will be understood, however, that the other amines are capable of closely similar performance.

The antimony-alkanolamine complexes of the invention are prepared by simply mixing a suitable antimony compound with an excess of the amine. Typically, antimony chloride is gradually added to the amine with stirring. A ratio of three to six parts alkanolamine to one part of the antimony compound is preferred. The reaction proceeds rather slowly with a smaller excess of the amine and nothing is gained by having more alkanolamine present, although the reaction takes place in the presence of any desired amount of the amine. A small amount of water does not interfere with the reaction. It is neither necessary to dehydrate the triethanolamine nor to maintain otherwise anhydrous condition.

The reaction is exothermic and proceeds rapidly after having been initiated. The start of the reaction can be hastened by initial heating, but proceeds spontaneously at any reasonable ambient temperature. It is preferred to heat a mixture of triethanolamine and antimony trichloride to about 40 C. to initiate the reaction. The temperature ultimately reached by the reaction mixture is not critical and depends upon the amount of heat that is lost by the reaction mixture to the environment. It is generally preferred not to exceed the boiling point of the amine.

The complex compounds formed in the reaction have not been isolated yet from the excess of the amine in which they are dissolved,.and their precise composition is not known. Such knowledge, however, is not essential to the invention, and the solutions of the complex compounds in the amine excess may be added directly to a silver plating electrolyte. An antimony content of about five percent by weight in the complex solution is convenient in normal plating practice.

Antimony trichloride is preferably employed in preparing the antimony complexes of the invention. It rapidly reacts with the amines to form a readily soluble complex compound. Freshly precipitated antimony oxide hydrate also dissolves in an excess of triethanol-amine, but heating to C. for one hour is required. The solution of the complex antimony compound in an excess of triethanolamine which is obtained thereby produces bright, hard alloy plates from a silver cyanide electrolyte indicating that the nature of the anion originally associated with the antimony is not of primary importance, but the brightness of the electrodeposit achieved with antimony chloride under otherwise analogous conditions is superior to that available with the oxide hydrate.

The amount of antimony that should be added to a silver cyanide electrolyte in the form of amine complexes for producing a significant improvement in brightness and hardness should be at least 0.01 gram per liter. Nothing is gained by increasing the antimony concentration beyond 10 grams per liter. Under most practical conditions, operation with antimony concentrations between 0.2 and 3.0 grams per liter yields best results.

The brightness of the silver-antimony alloy deposits produced by the method of the invention can be further improved by the addition of divalent selenium compounds which are known brighteners in silver cyanide electrolytes. Potassium and sodium selenocyanate are typical of such brighteners.

An agitated electrolyte made up to contain per liter, 30 grams of silver, about 100 grams alkali metal cyanide, and an amount of antimony as the amine complex as illustrated in the following examples, typically produces at least semi-bright alloy deposits on a conductor over a range from 0.2 to 1.5 amperes per square decimeter (amps./dm. of cathode surface the deposits having a hardness of 160 to 22-0 kp./mm. When as little as 0.001 gram sodium or potassium selenocyanide is added, mirror bright deposits are produced from 0.1 to 2.5 amptt/dm. without loss in hardness.

The following examples of electrolyte compositions are further illustrative of the invention, but it will be understood that the invention is not limited to the examples.

Example 1 G./ 1. Silver (as sodium silver cyanide) 30.0 Free sodium cyanide 110.0

Sodium carbonate 25.0 Antimony (as reaction product of SbCl with triethanolamine) 0.5

Example 2 Silver (as potassium silver cyanide) 35.0

Free potassium cyanide 120.0

Free potassium cyanide 120.0

Potassium carbonate 30.0 Antimony (as reaction product of SbCl with diethanolpropanolamine) 1.0

Example 6 Silver (as potassium silver cyanide) 30.0

Free sodium cyanide 100.0

Sodium carbonate 30.0 Antimony (as reaction product of SbCl with N-n-butyl-diethanolamine) 0.8

The various antimony-amine complex solutions added to the electrolytes in the examples contained approximately Sb by weight.

Hard alloy deposits which were at least semi-bright were obtained in all instances in the current density range indicated above, and the brightness and bright plating range could be improved by the addition of divalent selenium compounds. The brightness and bright plating range of the electrolyte of Example 1 were superior to those achieved in the other examples under otherwise analogous conditions.

While the invention has been described with particular reference to specific embodiments, it is to be understood that it is not limited thereto, but is to be construed broadly and restricted solely by the scope of the appended claims.

What is claimed is:

1. An aqueous alkaline silver plating electrolyte solution for the deposition of hard silver deposits consisting essentially of silver cyanide and at least 0.01 gram per liter of a preformed complex compound formed 'by the reaction of an antimony compound with a tertiary amine, said tertiary amine having the formula:

wherein R is selected from the group consisting of lower alkyl and a radical of the formula (C H )-OH, R and R are radicals of the last mentioned formula and n in said formula is an integer between 2 and 6, said antimony compound being reacted with the amine in the ratio of 3 to 6 parts by weight of the amine to 1 part by weight of the antimony compound; said reaction being conducted at a temperature between 40 C. and the boiling point of said amine.

2. An aqueous alkaline silver plating electrolyte solution for the deposition of hard silver deposits consisting essentially of silver in the [form of a complex cyanide and at least 0.01 gram per liter of a preformed complex compound formed by the reaction of an antimony compound and a tertiary amine, said antimony compound being selected from the group consisting of antimony oxide, antimony oxide hydrate and antimony trichloride, said tertiary amine being a compound of the formula:

whereinR is selected from the group consisting of lower alkyl and a radical of the formula (C,,H )OH, R and R are radicals of the last mentioned formula, and n in said formula is an integer between 2 and 6, said antimony compound being reacted with the amine in a ratio of 3-6 parts by weight of said amine to one part by weight of said antimony compound; said reaction being conducted at a temperature from about 40 C. to the boiling point of said amine.

3. An aqueous alkaline silver plating electrolyte solution according to claim 2 wherein said antimony/ amine complex is present in an amount ranging from about 0.01 gram per liter to about 10 grams per liter.

4. An aqueous alkaline silver plating electrolyte solution according to claim 2 wherein the concentration of said antimony/amine complex compound is between 0.2 and 3.0 grams per liter.

5. An aqueous alkaline silver plating electrolyte solution according to claim 2 wherein said tertiary amine is a trialkanolamine.

6. An aqueous alkaline silver plating electrolyte solution according to claim 2 wherein said tertiary amine is triethanolamine.

7. An aqueous silver plating electrolyte solution according to claim 2 which further contains a compound of divalent selenium as a brightener.

8. An aqueous alkaline silver plating electrolyte solution according to claim 7 wherein said brightener is an alkali metal selenocyanate.

9. A method of preparing a hard silver alloy deposit on a conductive article which comprises making said article the cathode in an aqueous alkaline electrolyte solution, said electrolyte solution containing silver in the wherein R is selected from the group consisting of lower alkyl and radicals of the formula -(S,,H )-OH, R and R are radicals of the last mentioned formula and n in said formula is an integer between 2 and 6; said antimony compound being reacted with said amine in a ratio of 3-6 parts by weight of the amine to one part by Weight of the antimony compound; said reaction being conducted by contacting the antimony compound and tertiary amine at a temperature of about 40 C. to the boiling point of the amine.

10. A method according to claim 9 wherein the current density at said cathode is between 0.1 and 2.5 amperes per square decimeter.

References Cited UNITED STATES PATENTS 2,330,962 10/ 1943 Feinberg 260-446 2,555,375 6/1951 Ruemmler 204-43 2,735,808 2/1956 Greenspan 204-43 XR 2,777,810 1/ 1957 Ostrow 204-46 2,801,959 8/1957 Du Rose 204-45 2,817,628 12/1957 Breining et a1 204-45 3,215,610 11/1965 Skaliks 204-45 XR 3,219,558 11/1965 Foulke 204-46 JOHN H. MACK, Primary Examiner. G. KAPLAN, Assistant Examiner.

US. Cl. X.R. 

